This invention relates to compound engines and in particular to a turbofan-ramjet engine providing for optional duct burning in the turbofan mode. A turbonfan-ramjet engine is disclosed in U.S. Pat. No. 2,952,973 and other composite power plants including turbojet and ramjet combinations are set forth in the following U.S. Patents: U.S. Pat. No. 2,896,408; U.S. Pat. No. 3,091,082 and U.S. Pat. No. 3,280,564.